小通道氮气-水两相流三谱切片波动特性及其流型表征

The sliced trispectrum fluctuation characteristics and flow pattern representation of the nitrogen-water two-phase flow of small channel

将三谱切片与波动特性分析方法相结合,组建了一种新的非线性分析方法,并讨论了时间序列长度与快速傅里叶变换(FFT)长度对三谱切片的波动特征值的影响,发现在无噪声干扰情况下,序列长度与FFT长度与矢量类间距值成正比,在有噪声干扰情况下,近似成反比关系.将该分析方法应用到分形序列(Brown)、混沌序列(Lorenz)和周期序列(正弦),检验了波动特性方法的抗噪能力和表征复杂度能力.结果表明:该波动特性分析方法较其他功率谱分析方法对分形和混沌序列具有较好的抗噪能力,而对周期序列的抗噪能力相对较弱;该波动特性方法对序列内在复杂度的表征具有较好的效果.在此基础上,对水力直径为1.15mm的矩形小通道(w×h=2mm×0.81mm)中的矩形通道内氮气-水两相流型的差压信号进行了研究.通过对流型差压信号三谱切片的分析揭示了不同流型的主振荡模式二次耦合现象,提取不同流型三谱切片的波动特征值,实现了小通道氮气-水两相流典型流型的准确识别,同时也为其他不同介质的多相流动特性分析与流型辨识提供了一个新的思路.

A new method of nonlinear analysis is proposed by combining the sliced trispectrum method with the fluctuation characteristics, and the influences of the length of the time sequence and fast Fourier transform （FFT） on the fluctuation characteristic value of sliced trispectrum are discussed. It is found that in the absence of noise, the length of sequence and FFT are proportional to the vector distance value; in the presence of noise, it is approximate inversely related. In order to test the anti-noise ability and characterize complexity ability of the fluctuation characteristics method, the proposed method is applied to fractal sequence （Brown）, chaotic sequence （Lorenz） and periodic sequence （sine signal）. The results show that compared with other power spectral method, the method of the fluctuation characteristics has good noise immunity of fractal sequence, and the anti-noise ability is relatively weak with periodic sequence; but the fluctuation characteristic theory of sequence internal complexity representation has a good effectiveness. On this basis, the differential pressure signals of nitrogen-water two-phase flow in small rectangular channel （w × h = 2 mm × 0.81 mm） are studied. By analyzing the differential pressure sliced trispectrum of flow patterns, the secondary coupling phenomenon of main oscillation mode of different flow patterns is established. The fluctuation characteristic values of the sliced trispectrum of different flow patterns are extracted to accurately identify the typical flow patterns of small channel nitrogen-water two-phase flow. At the same time, the fluctuation characteristic theory can be used to provide a useful exploration for the further investigation of flowing mechanism of multi-phase flows.